Electrostatic apparatus



Oct. 10, 1950 s. GILMAN 2,525,347

ELECTROSTATIC APPARATUS Filed Feb. 9, 1945 2 Sheets-Sheet 1 WITNESSES: INVENTOR S'arnue/ 6/7/0620.

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ATTORNEY Oct. 10, 1950 s, GILMAN 2,525,347

ELECTROSTATIC APPARATUS Filed Feb. 9, 1945 2 Sheets-Sheet 2 .g' a A, T

1 g fig: A5 I k u/ Q q /00 gig M /00 E fi M E\ 0 Pas/five l/o/ aye WITNESSES: I INVENTOR -5amue/ 6/7/1762 ATTORNEY Patented Oct. 10, 1950 2,525,347 :ELECTROSTATIC APPARATUS Samuel Gilman, Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, a corporation of Pennsylvania 1 Application February 9, 1945, Serial No. 577,021

j 22 Claims. (Cl. l837) This invention relates broadly to apparatusfor providing a charged spray of discrete non-gaseous particles; and, specifically, to a nozzle-device, haVing an electrode associated with it, for

producing a spray which is electrically charged.

In another sense,-the'invention is directed to improvements inelectricaldust-precipitators of a type shown in the Gaylord W. Penney Patent No. 2,357,354 of September 5, 1944; which 'uses a means for producing a charged spray.- Such an improved dust-precipitator, in accordance with my invention, has a modified operation with an improved efliciency. i

In the removal of dust-particlesfrom a flowing gas-stream, in accordance withthe aforesaid patent, the gas-borne dust-particles are first given an electrical charge of a'predetermined potential-polarity, and then are precipitated by means of an electrically-charged spray of very fine drops through which the'dust-carrying gas is passed. The spray-dropsare charged with a potential-polarity opposite tothat given to the dustparticles So as to attract and combine with them. The gas is cleaned by subsequently separating the spray with the attached dust-particles from the gas-streams: ,q l

My invention seeks ;to improve upon such electrical dust-precipitators. The aforesaid patent, while not limited. thereto, shows severalforms of equipment with which'a spray can be produced and electrically charged. The spray is obtained by providing a spraying-device having a liquid discharge or liquid" emitting opening at the end of a single tapered member, or a plurality of such openings associated with a single pipe-member. The spray-drops are charged inductively by having such member, at which the spra originates, serve as an electrode-means of opposite-potential-polarity with respect to'another electrodemeans relatively insulated therefrom so that an electrostatic field exists at -;the point at which the spray leaves the member. The spray-drops are electrically charged with a polarity which is opposite to that of the insulatedelectrode-means and to that on the gas-borne dust-particles.

In apparatus of this kind,-it;is-;desirable to provide as large a net or total charge as possible on the spray; but if the voltage or electromotive force between the oppositely charged electrode means is continuously increased, a point is reached in which this net total charge no longer increases but, on the contrary, ma actually decrease. This can be explained.- The relatively insulated electrode-means is close-to the path of the main part of the spra so that mist-particles l 2 bordering the spray actually impinge on, and some spray-drops are electrically attracted to, the relatively insulated electrode-means. The liquid collects on an electrode means and soon there is enough to form a plurality of large drops on this electrode-means, the drops becoming charged to the potential of the latter. If the electric field at this electrode-means exerts a sufficient force, the drop will be pulled out of Shape into a point and will discharge an ionizing current of charged matter which is of the same sign or potential-polarity as that of the relativel insulated electrode-means. This charged matter tends to neutralize the opposite charge on the spray to an extent depending upon the intensity of the total ionizing current coming from the drops. In extreme cases, the number of discharging drops and the intensity of their discharges may be sufiicient to actually reverse the polarity of the charge on the spray, practically nullifying any electrostatic dust-precipitating effect it might otherwise have.

' It is a further object of my invention to im prove an electrical dust-precipitator of a type described; b improving its means for producing a charged spray and also by arranging this means so as to aid dust-precipitation.

Hereinafter in the description, in order to read ily distinguish the drops collected on the electrode-means from those of the Spray, the former are referred to as drops and the latter as droplets, or particles. It should be understood that the drops are generally considerably larger than the droplets in the spray, and can be readily seen on an. electrode.

For producing a charged spray, any suitable means may be used. Several examples comprise a nozzle which directly emits the spray, as shown in Figures 1 and 2 of the aforesaid patent, and a pneumatic nozzle-device in which a gas, usually air, is used to break up a liquid into fine particles which the gas carries along in the form of a spray, as shown, for example, in Fig. 3 of the aforesaid patent.

In order to charge the spray-droplets, an intense electrostatic field is provided at the point or opening at which the spray originates that'ls, a high field-gradient is provided at such point. The relatively insulated electrode-means, which aids in providing this electrostatic field, is preferably close to the point and along the main path of the spray which flows past it, so that liquid necessarily collects on it. The liquid gives up its original charge to this electrode-means and is inductively charged thereby to the potential of the electrode-means so that the liquid becomes charged to a polarit opposite to that which this liquid originally had as part of the spray. Since the liquid is mobile, it can be moved about on this electrode-means by forces acting on it which result from gravit and from any electrostatic field established between the electrode-means and a region or surface of opposite polarity. Withoutthe improvement of m invention, the spray-charging electrostatic field is mainly that provided between the nozzle-tip from which the spray emits and the relatively insulated electrode-means. If this field provides a field-gradient at the electrode-means which is sufliciently high, the collected drops will be distorted and discharge an objectionable ionizing current, as described above in connection with the electrostatic dust-precipitator, thereb limiting the intensity to which the field can be raised under a given set of conditions'. 4 ;My .invention seeks toimprove upon the producing of a charged spray, p

. It is an object of my invention to increase the charge .thatcanbe imparted toa spra of discrete particlesg f t -is a iurther obj cct o f myinvention to provide apparatus for producingfa charged liquidspray. in which-the spray-droplets are highly charged-substantially at the source of the. spray, and the net spray charge is not thereafter decreased. v i r j v In accordance with preferred forms of my invention,-I- provide a construction which will introduce forces which will permit the s raycharginge ectrcstatic field tobe increased without introducing theobiectionable discharge -from thacollected dro s. "In some forms of my invention, I arrange theelectrode means so that the collecteddroos face'away from the oppositelycharged; nozzle-de ice-end spray. :In still anoth r f rm of m invention I- drain. off the collected liou d through a highs-resistance piping. mother obiectsgfeatures, innovations, elements and-.combinat onsof myinvention will be discernib e .fromzthefollowing descri tion which is to be t ken in con unction with the accompanying schematic drawings. I

---In the drawings,.-Which are not to scalez' Fig re 1 is a vert cal sectional view of an embodiment of my invention:-.

"-Fi ..2-is a vertical sectional view of part of an, el ctrical dvst-orec oitator embodying another form of my-invention;

Fig. 3 is a view simil r to Fig. 2, but of still another formof my in entionz 1 1 Fig. 4 isahorizontalsectional view, taken sub stantlally on the line IV--IV of Fig. 3;

Fig. 5 is a verticalsectiona view ofan electrical: dvst-nrecioitator embodying'a further form ofimyinvention:

Figs. 6 and '7 are a plan and a vertical sectional view,':=resoectively,oi' an electrode utilizable in an application of my invention; J

-:Fig.-' 8. is a 'plan'view of another form of electro'de;- 1'" A? Fig. 8A is a vertical sectional view of an electrical dust-precipitator embodying the electrode of Fig. 8;? "I H 'Fig. 9 is a vertical sectional view of an electrical dust-precipitator embodying still another form of my invention;-

*Figs. 10 and 11 are sectional views, taken substantially on the lines X-X and XI-XI, respectively, of Fig. 9;

.- sulated electrode.

A device for producing a highly-charged liquid-spray operating in accordance with the principles of my invention is shown in Figure 1. For convenience, the spray-producing nozzle-device has been shown as a metal pipe 2 having a conical metallic spray-discharge nozzle 4 which converts a liquid supplied under pressure to the pipe into a conical spray 8 which so asses through a' toroida or ring-shaped electrode 8 that the visible outline of the spray clears the inner periphery of the electrode. The electrode 8 is relatively insulated from the spray-discharge nozzle 4 but arranged as closely as convenient to the extreme opening or point of the spray-discharge nozzle 4 from which the spray comes. The sepa ration is usually determined by the magnitude of the voltage applied between the spray-discharge novze 4 and the electrode 8, and should be such that there is no danger of objectionable breakdown or arc-over. A source of electric power, indicated as a direct-current battery 19, has one end connected to the nine 2 and the other to the electrode 8 for maintaining the nozzle-tip and the electrode 8 at opposite potential-polarities. Accordinglv, the nozzle-tip is, in effect, an electrode wh ch is charged o positely from the electrode 8. Preferably; the whole s ray-producing device, which includes the pi e 2 and nozzle 4, is grounded, as indicated at I 2.

In the operation of e uipment having only the parts thus far particularly described, there usually is an extremely fine mist along the outside of the spray, or other spray-liquid which reaches the electrode 8. Such liquid can accumulate on the electrode, forming large distinct drops thereon. If the electrostatic field between the spraydischarge nozzle 4 and electrode 8 is sufdcient y great, the drops will be attracted to the inner side of the electrode and be deformed so as to point toward the charged sprav 6. Since the drops are in contact with the electrode 8, they become charged with the same sign and consequently discharge in a manner for introducing charged matter of the same potential-polarity into the spray region, this potential-polarity being opposite to that originally imparted to the spray-droplets. Such an effect limits the charging potential to which the electrode 8 may be raised with respect to the nozzle or electrode 4.

This is illustrated in Fig. 15 in which the ordi nates represent the net charge per cubic centimeter of spray-liquid and the abscissae the voltage or electromotive force between a nozzle-tip and a relatively insulated spray-charging electrode of a device along the lines of Fig. 1 having only such parts as electrodes. At first, the total charge on the spray after leaving the nozzle-tip increases as the voltage is increased. The volt age can be increased for increasing the spacecharge of the spray, that is, the net spray charge, but a range is reached where the drops on the insulated electrode face toward the spray and are drawn into points discharging into the spraythe spray-producingrneans 26.,

region. The net spray charge then levels off with greater voltages. *"A condition I is ultimately reached, indicated at beyond which any further increase in the voltage increases the discharge from thedrops more than it adds to the charge of the liquid coming from the nozzle-tip. The result is that the net or total charge in the spray is lowered with further increases in voltage beyond M. The maximum point, corresponding to M, is determined by the physical setup of a particular apparatus,--but, in general, the curve of ,Fig. is found to be followed where'a nozzle-tip and an electrode-means, or the equivalent, con- 'stitute the charged-spray-producing means. In accordance with my invention; means is provided which opposes or overcomes such drop-discharge effect, altering'the curve of Fig. 15 so that the net spray charge still increases with increases in yoltage beyond Ml To this end, n Fig. '1 I provide another rin shapedelectrode M which is closer to the electrode 8, than it is to thespray-discharge nozzle "41" By grounding the electrode 14; as indicated at l6, an'electrostaticfield is established between the electrodes 8 and I4, which 'also acts: on the collected drops., The electrostatic forces which lresult from" the' reaction of a charged drop and the field betweenthe electrodes 8 and 14 act on the drops but those forces are opposed by the forces which result from the reaction of the charged drop and th'field between the electrode .8, on the one hand. and the combined nozzle 4 and spray 6 on the other hand. By creating an adequate field gradient at the electrode 8 directed toward the electrode 14, the drops are pulled to the outside of the electrode 8, become distorted into points, and electrically discharge toward the electrode l4 instead of toward the spray. Such drops are indicated'at l8, five of them being arbitrarily sho'wnin Fig. 1. With the connections shown, increasing the voltage between the sprayproducing means, as one electrode, and the relatively insulated electrode8 also increases that between the electrode I4 and the electrode 8. 'By

making the electrode larger than the electrode 3 and arranging it below the electrode S, the discharge is in a direction away from the spray, so thatit can not adversely;afiectnthenet charge on the spray. 23

- ,-In Fig.- 2, I showtheadaptation of my invention to an electrical dust-precipitator such, as shown in the aforesaid Penney patent. .A

grounded circulars-metal gas-,duct .20 .includes therein an upstream dust-charging means or ion- ;izer comprising 'a metalicylinder e22 concentric "supported within flthe duct 2 1] by an. insulator 38 in suitable relation to the tip of the spray-pro ducing meansZGM The ringelectrode 28 is maintained at a highpositive potentialpolarity r with respect to thespray-producing means 26 through an insulated conductor a 32 passing :through. the gas-duct means, so that the spray34' is charged. Any drops whichcollect-on the electrodez28; by impingement or: by electrostaticattraction, are

made to discharge .;to thegrounded. duct, by-

wouldotherwise reduce the net charge in the spray now discharge toward the gas-duct 20, away from the spray region.

Causing the drops to discharge toward the duct 28 has the further advantage of aiding the charging of the dust-particles in the part of the gasstream passing between the duct 20 and the electrode 28, because the charging action of the pointed drops is the same as that of the ionizing wire 24, and such part of the gas-stream has not yet mingled with the charged spray.

- Grounded field-afiecting electrodes 36 are provided below the ring-electrode 28 for keeping down the space-charge within the spray after the spray has spread across the gas-duct. The

nearest electrode 36 may be farther from the electrode 28 than the nearest point of the grounded gas-duct 20.

If desired, the grounded gas-duct of an electrical dust-precipitator, such as shown in Fig. 2, can be provided with a curved section acting as an electrode-means for providing the secondary electrostatic field extending to the insulated electrode. This embodiment is shown in Fig. 3 in which an ionizing wire 38 and associated electrode-means 48, within the metal gas-duct 42, provide a dust-charging means in an upstream zone in which gas-borne dust-particles are charged. The downstream precipitating zone comprises, briefly, any suitable grounded sprayproducing means 44 and associated insulated electrode 46. A curved electrode-means 48 is provided as part of the gas-duct 42, the electrode means 48 being coaxial with the insulated electrode 46. r

The dust-particles can be charged positively and the spray-drops negatively, or vice versa, as more fully explained in the aforesaid Penney patent. To indicate these alternatives, the apparatus, of Fig. 2 shows positive ionization used for charging the gas-borne dustmarticles, while the spray, itself, is changed negatively; whereas in Fig. 3 the potential-polarities are reversed so that the gas-borne dust-particles are negatively chargedand the spray-droplets positively charged. I

Fig. 5 shows a further embodiment in which the relatively insulated electrode is formed with an outwardly flared conical skirt 62. I Gravity can pull the mobile collected liquid on the electrode to the bottom of the downwardly ex tended skirt so that collected drops are farther removed from the electrical center of the spray 63 and the tip of the spray-producing means than they are from the duct 64. Consequently the spray-charging field and the field established between the electrode 60 and the charged spray exerta total force on the drops which is, less than that resulting from the field between the bottom of the skirt 52 and the duct 64., Because the drops no longer discharge into the spray, a much greater charge can be given to thespray than would be possible if the relative strength of the forces exertedby the fields were reversed,

asis theicaseinzthei aforesaid Penney patent. The area through which'the gas passes between the relatively .insulatedelectrode, such as 62 of Fig. 5, and the "gas-duct can be increased by using electrodes such as shown in Figs. 6 through 8. .In these embodiments, the relatively insulated electrode is provided with a series of prongs 61 asshown in Figs. .6 and .7, or with a downwardly extending scalloped skirt 63, as indicated in Fig. 8. The'liquid collecting on the electrodes travels downwardly to a lowermost point because of gravitational force..." 1 1 c Any suitable construction'bfinsulated electrode-meansandany suitable arrangement of associated electrode-means having an opposite charge for producing the auxiliary secondary field can be used so long as the collected drops are allowed to discharge away from or are led away from the region of the spray.- This region is that occupied bythe-spray until after ithas mingled and electrically jattractedthe charged dust-particles. It'is not possible to describea precise boundary for the region of the spraybut when the .drops point away from this region generally they canzdischarge ,harmlessly into'some other region. so as not to interfere with the attraction between the charged spray-droplets and dustparticles. In the electrical precipitators shown in Figs. 1 to 5,this discharge of the liquid-drops is usedto added advantage for increasing the total charge on the duct-particles.

In Fig. 9, I show still another form of electrical dust-precipitator which embodies the foregoing feature of my invention, and, in addition, provides a difierent form of relatively insulated electrode-meansfor inductively charging the liquidof. the spray as it comes from the spray-producing means. It hasmor special advantages in a laterally large gas-duct or for providing a charged'spray in large quantities.

. The dust-charging means in Figs. 9 to 11 comprises a plurality of spaced grounded relatively large tubular electrodes between which relatively fine ionizing wires'lZ are insulatedly supported. On the downstream side of this dustcharging zone, a dust-precipitating means is provided comprising .a .means for producing a charged-spray,j.the last means being indicated in its entirety by the reference numeral 14. The charged-spray-producing means 14 comprises any suitable equipment which emits a liquidspray, and is shown as a metal pipe-member 18 provided with a plurality of spray-discharging metal nozzles 18 spaced along its length. The tips of the nozzles-are kept at ground-potential by grounding the pipe-16 or='conductively associating it with the grounded metal gas-duct 80. {I'he spray fromthe nozzles '.'8 passes between a pair of spaced straight semicylindrical insulated electrodes 82 whichare given a" relatively high potential through insulated conductors 84 and any suitable electricalpower source. The potentialpola'rity or the'electrodes 82 and the ionizing wires "I2 is the same, and is opposite to that of the electrodes'm and -nozzles I85 1 Liquid drops collecting on the electrodes 82 are caused todischarge' toward the grounded gas- 'duct'-80- by -having a lengthwiseside of each electrode 82 suliiciently close to a side 86 of the gasductz I In l2, I haveshown an embodiment similar to tnator Figsi 9 to 11, except that the action of gravityf iri 'removingfthe discharging drops 'i'arther 'from the spray-charging region is in- .creased'. This is done by sloping the spaced electrodes which areequivalent to the electrodes 82 of Figs. 9 through 11. Such sloping permits the spacing between the lengthwise side of the electrodes and the corresponding sides of the gasduct to be increased because the drops flow to the lowermost ends of the electrodes.

Figs. 13 and 14 show a further form of my in vention, using spaced cylindrical elongated relatively insulated electrodes I09 between which a metal spray-producing means I82 establishes a spray. In this'embodimenathe spray-producing means has been shown as pneumatic, comprising a. grounded liquid-supply pipe-member I04 and an air-supply pipe-member I06 connected to a plurality of spray-nozzles 188, having outlet tips H0. Liquid flows centrally through each spraynozzle through a passage 1 12. Air under pressure flows in a conical passage H4 which is around the passage H2 and is tapered to the outlet tip no for providing a spray which passe between the insulated electrodes I00.

The electrodes H30 are sloped and the lowermost end of each is provided with a small catchbasin H6 having adrain-opening to which a drain-pipe H8 is connected for draining off liquid'collected on the electrode. The drain-pipe H3 is of some insulating material so as to provide a high-resistance path for the draining liquid which flows into a grounded container 20.

In embodiments utilizing a high-resistance drain, the collected liquid loses its charge by leakage, so that electrical discharges from distorted liquid drops on the electrodes are greatly minimized, or entirely eliminated. In embodiments which do not use a drain, collected liquid can fall from the relatively insulated electrode after they form large enough drops. This loss of collected liquid, which is desirable, i augmented in cases where the electrode, which provides the spray-charging electrostatic field, has a portion which slopes downwardly, as, for example, the skirted embodiments shown in Figs. 5 through 8, or the straight sloped electrode embodiments shown in Figs. 9 through 14; the latter, however, being the subject matter of my divisional appli cation Serial No. 705,332, filed October 24, 1946.

The application of my invention to a vertical spray-charging electrode in a horizontal enclosure is obviously much more simple since all the collected liquid will usually drain to the bottom of the electrode. A discharging region or draining means can be provided for the drops just at that place.

Making certain assumptions, it can be shown that the minimum field gradient in volts per centimeter required for distorting a collected spherical drop, so that it becomes a point discharge, is given by the formula:

where T is the surface tension of the liquid in dynes per centimeter and a the radius of the drop in centimeters. However, this formula is subject to wide variation because of the difiiculty of'- accurately setting up the phenomena of charging a spray.

I'have found that the use of substantially straight electrodes, either cylindrical or semi cylindrical, such as shown in Figs. 9 through 14,

or other cross section, in equipment for charging a spray, is a considerable improvement over ring-type electrodes, particularly if used with spray-nozzles of a pneumatic type along the line shown,.for example, in Fig. 14.

JPNF, set-up No. 12, described in a catalogue Tidentified as Sprayin System Nozzles and Related Products, catalogue No. 22 of the Spraying System Company, Chicago, Illinois, an improvement of as much as 200% and above in the charge given to the spray was obtained over that obtained with'the specific non-pneumatic type of spray-nozzle and rin electrode specifically described in the aforesaid Penney patent. In one embodiment of my invention, the top surfaces of the straight electrodes were substantially on the same level as the extreme tip of a spray-discharge nozzle, being not more than A" below it. The pair of electrodes were parallel and spaced about 1% apart, with a spraytip mid-way'between them. By sloping the electrodes about 20 to the horizontal, instead of keeping them horizontal, very efiective draining of collected liquid was provided, permitting a much higher voltage between the spray-nozzle and the electrodes before objectionable drop discharges occurred.

The diameter of the straight electrodes and their spacing affect the size of the collected drops and the amount of charge that can be given to the spray. With a constant voltage across the tubular electrodes and the spray-discharge nozzle, increasing the separation of the electrodes affects the field-gradient at the nozzle tip and at the surface of the electrodes. The factors affecting the field-distribution are, however, so varied and complex that an exact analysis is hardly practical. Various grounded surfaces around the nozzle and the relatively insulated electrodes, as separate electrode means, obviously will change the field lines. Even the character and angle of the spray have their effect. However, experiments indicated that for a, particular apparatus there appears to be an optimum spacing for straight electrodes at which a maximum charge is imparted to the spray.

While I have described my invention in forms which are now preferred and have shown the novel spray-charging equipment portion of my invention applied/to an electrical dust-precipitator, using water as the spray-liquid, my invention is not so limited either to use with water or in an electrical dust-precipitator. Any liquid or substance consisting of,'or capable of being broken into, discrete particles and which has some electricity-conductive or semi-conductive qualities, so that its drops or particles can be charged, can be used for providing the charged-spray. It is also obvious that the principles of myinvention can be embodied in forms and modifications other than those herein described.

j I claim as my invention:

1. A precipitator device of' a class described comprising, in combination, a duct-means for a gas-stream, charging-means for charging gasborne dust-particles, a liquid-spraying device on the downstream side of said charging-meansan electrode in said duct-means insulated from said liquid-spraying device and arrangedjin proximity to the path for the spray from said liquid: spraying device, said electrode-means being spaced from said duct-means so that a portion of the gas-stream can flow therebetween; said charged spray on the downstream side of said charging-means, comprising relatively insulated oppositely-chargeable spray-means and electrade-means, the electrode-means being so constructed and arranged that the spray from said spray-means passes in proximity thereto and then spreads across said duct-means, said electrode-means comprising a ring-shaped member provided with a depending outwardly directed extension which terminates short of said ductmeans at a place where the spray is not spread across the duct-means.

3. Apparatus for providing a utilizable charged spray, comprising a nozzle-means, a ring-shaped electrode insulated and spaced from said nozzlemeans so that a spray from the nozzle-means passes through it, the space between said electrode and nozzle-means being otherwise substantially free, and an additional electrode insulated from and spaced from said ring-shaped electrode, one of said electrodes having an irregular contour on the side toward the other electrode, said electrodes being separated a lesser distance than the spacing between said nozzle-means and said ring-shaped electrode.

4. A precipitator device of a class described for utilizable gas-cleaning of a gas-stream, comprising the combination with a gas duct for a substantially vertical gas-stream, having therein dust-charging means for charging gas-borne dust-particles; of means for subsequently removing charged dustparticles from the gas-stream comprising charged-spray-producing means including an electrode and a spraying device with a substantially free space vertically therebetween, and potential-applying means for establishing an electrostatic field in said space, with a field-gradient at said electrode and at said spraying device, said charged-spray-producing means providing a charged liquid-spray on the downstream side of said dust-charging means, said electrode being so disposed with respect to the spraying device that the charged liquid-spray can pass near said electrode with spray-liquid collecting thereon, forming liquid-drops, the spacing, configuration and potentials being such that the tendency of the field gradient at said electrode in a direction toward said space to cause liquid-drops on said electrode to be deformed and to discharge toward said space, is overcome, whereby the liquid-drops cannot significantly afiect the net charge on the dust-precipitating liquid-spray.

5. A precipitator device of a class described for cleaning a gas-stream, comprising a gas duct for a substantially vertical gas-stream, having therein charging-means for charging gas-borne dustparticles, means including a spraying device for providing a charged liquid-spray in a region of the downstream side of said charging-means, said means including a first electrode relatively insulated from said spraying device, there being a substantially free space in the path for gas flow between said first electrode and spraying device, said gas duct including an electrode-means insulated from and spaced from said first electrode on the side thereof away from said region, and potential-applying means for oppositely charging the first electrode with respect to said spraying device and with respect to said electrode-means, the spacing, configuration and potentials of said spraying device, said first electrode and saidelectrode-means being such that the tendency of the field gradient at said first electrode in a direction toward said space to cause liquid on said'first electrode to be deformed and to discharge toward said region; is overbalance'd by the action on such liquid of th'efiel'd gradient at said first electrode in a direction toward said electrode-means.

'6. Means for producinga charged liquid spray, said means including an electrode and a spraying device spaced therefrom for producing a charged spray in a spray-region associated therewith, the electrode being so disposed. with respectto the spraying device that spray liquid can collect on the electrode and form liquid-drops, potential-- applying means to provide a field-gradient at said electrode in a direction toward said spray-region and a field-gradient in a direction away from said 'sp'ray regi'on, the spacing, configuration and potential of said spray device, electrode and potential-applyin'g means being such that the tendency of the first said field-gradient to cause liquid on said electrode to be deformed and to discharge to said spray-region, is overcome.

7.- A precipitator'device of a class described for utiliz'able gas-cleaning of a gas-stream, comprising the combination with a gas duct having therein dust-charging means for charging gasborne dust-particles, of means for subsequently removing charged dust-particles from the gas-- "stream in the gas duct, comprising means in eluding ai ing-like first electrode and a spraying device having'a' subst-antially free space therebetween in the direction for gas flow, the electrode being so disposed with respect to the sprayin'g device that spray liquid can collect on the electrode," forming liquid-drops, and a second electrode between said first electrode and a part of "said gas duct, said second electrode being arrangedso-that'said first electrode is closer to said second electrode than saidfirst electrode is to the "of said gas-duct and to said spraying device, saidfirstielectrode being insulated and said spraying device, gas duct and second electrode being grounded. v

8.;1A precipitator device of a class described for utilizablegas-cleaning of a gas-stream, comprising'j the' combination with a gas duct having th'er'ein1 dust-charging means for charging gasbor'ne fdustparticles, of, means for subsequently removing fch'ar'g'ed fdust-particles from the gasstreamjin jthef'gas duct, comprising electrode meari's'iricluding'a ring-like portion and a spraym nevi e having a substantially free space therebetween inftlie 'direction for gas fiow, the 'ring likeportion'being so disposed with respect to ,the,spraying device that spray liquid can collect on, the ring-like portion, forming liquid drops, and'a plurality of distinct field-afiecting members fatfdifier ent places in the space between said ringlike'portion' and gas duct.

9 Means for producing a charged 'spray'cornp'ri's'ing a spraying means for establishing 'a spray orginatingat'a point, anelectrode insulated from said point, said electrode having'a ring-like porition' about said pointan'd a'plur'ality or spaced distinct portions extending outwardly in directions toward'a su'rfacecharged oppositely from sai'd'electrodef and away from'said point.

l0. 'Meansfor producing a charged spray, iconiprisinga spraying means for establishing aspray originating'at a point, anelectr ode insulated from said point, having a ring-like portion about said point, said j'electr'ode having a. skirt portion extending outwardly in a direction toward a surface charged oppositely from said electrode and away from said point,

11. invention including that defined in claim 10 but characterized further by'the edge of said skirt portion having a plurality of distinct points. i

12. A method of increasing the net charge of a charged spray established between a point from which a spray emits and a pronged electrode en'- tirely below said point for forming an electrostatic field therewith, which method comprises the. step of gravitationally outwardly forcing all of the liquid collecting on said electrode to positions removed from the region of the charged spray; the liquid flowing outwardly on said prongs. l g

13.3'A method of increasing the net charge of a charged spray established between a point from which a spray emits and an electrode near said point for forming an electrostatic field therewith for charging the spray, which method comprises the step of electrostatically deforming drops collectedon said electrode into points discharging ina direction toward asurface charged oppositely from said electrode and away from the region of the charged spray. g r

14. A method of increasing the net charge of a charged spray established between a point from which a spray emits and an electrode near said point fori orming an electrostatic field therewith for charging the spray, which method comprises the step of establishing field gradients at said electrode, with the field gradient at said electrode in a direction toward said spray being less than the field gradient at said electrode in a direction a a f m. s i s a a d t wa a Surface charged oppositely from said electrode.

15. 'A precipitator device of :a class described for cleaning a gas-stream, comprising the combination of an upstanding gas duct, and dustcollecting means for providing afdust-collecting charged liquid-spray extending downstream in a region in said gas duct, said means including a spraying device, a first electrode insulatedly spaced downstream from said spraying device, and a voltage source connected between said first electrode and said spraying device; of a second electrode in sulatedly spaced from and facing a side of gamers; electrode, said side facing away from said region, and potential-applying means for oppositely'chargingsaid second electrode with respect to said first electrode, the spacings, configuration and potentials in said dust-eolleeting means providing field gradients along said side of the. first electrode which are'inore intense than the field'g'radients'alongthe side of the first electrode facing toward said region.

16. Means forproduc'ing a eharged liquid-spray into a spray-region, comprising aspra'y-produc- 'ing device, a'pair of relativelyinsulated electrodes spaced'along thespray-r'eg'ion and electrically oppositely chargeable whereby to; chargeth'e spraydroplets, and voltage supplying'rneans to'provide a voltage between saidelectrodes so'that "a first of'theni has apotential p'olarityi opposite to that of the second eleotrode "and to that imparted to thespray-droplets, said 'firstelectr'ode being located'so that'spraylidiiid can collect thereon, said voltage-supplying means supplying sufiicient voltage'to'provideia tendency ordinarily to deform a plui'ality'of drops collected onsaid first electrode into a plurality of points which electrically discharge toward the spray, the points being at different places along said first electrode, in combination wane third electrode insulatedly spaced from said first electrode 'on the side away from said spray regiOn, and means comprising voltage supplying means to provide an electric field between said first electrode and the said third 8160-:

trode, with said third electrode having the same potential-polarity as said second electrode, the spacings, configurations and potentials of said electrodes and voltage-supplying means being such that the field-gradient at said first electrode in a direction toward said third electrode substantially overcomes the aforesaid tendency to deform said drops.

1'7. Means for producing a charged spray, comprising a spraying means for establishing a flaring spray in a spray-region, an electrode below and insulatedly spaced from said spraying means, means for electrically charging said electrode so as to provide a potential thereon for an electric field to charge said spray, the field providing a first field gradient along a first side of said electrode which side faces toward the spray, an electrode means comprising a metallic member spaced from a second side of said electrode, the second side facing away from said spray-region, and means for electrically charging said metallic member so as to provide a potential thereon which is opposite from that on said electrode, the spacing, configuration and potentials of said electrode and metallic member being such that the field-gradient at said first side of said electrode is less than that at said second side of said electrode.

18. A method of increasing the net charge of a spray between a point from which spray emits and a lower electrode near said point for forming an electric field therewith for charging the spray, which method comprises the step of establishing a second electric field along a side of said electrode which faces away from the charged spray with the field gradient at the electrode due to the second field being greater than the field gradient at the electrode due to the first said field.

19. Means as defined in claim 17 but characterized by said electrode comprising a ring and a metallic extension extending from said ring in a direction toward said metallic member.

20. Means for producing a charged liquid spray, comprising a spraying device and an electrode insulated therefrom, said electrode being spaced from said spraying device to provide a spray-space therebetween, said electrode having a first side facing in a direction toward said spray-space and a second side facing in a second direction away from said spray-space, a second electrode spaced from and insulated from the first said electrode, said second electrode facing 14 said second side of the first said electrode, the distance between said electrodes being less than that between said spraying device and first said electrode.

21. Means for producing a charged liquidspray, comprising a spraying device and an electrode insulated therefrom, said electrode being spaced from said spraying device to provide a spray-space therebetween, said electrode having a first side facing in a direction toward said spray-space and a second side facing in a second direction away from said spray-space, voltagesupplying means to provide a voltage between said spraying device and electrode providing a first field-gradient at said first side, a, second electrode spaced from and insulated from the first said electrode, and facing said second side of the first said electrode, and voltage-supplying means to provide a voltage between said electrode providing a second field-gradient at said second side, with the second field-gradient being greater than the first field-gradient.

22. Apparatus for providing a utilizable charged spray, comprising a nozzle-means, an electrode-ring insulated and spaced from said nozzle-means so that a spray from said nozzlemeans passes through it, the space between said electrode-ring and nozzle-means being otherwise substantially free and providing a sprayregion, and an additional electrode insulated from and spaced from said electrode-ring on a side facing away from said spray-region, said electrode and electrode-ring being separated a lesser distance than the spacing between said nozzle-means and said ring-shaped electrode, and means to place said nozzle-means and additional electrode at a common potential, and said electrode-ring at an opposite potential relative thereto.

SAMUEL GILMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS I Number Name Date 1,360,654 Littlefield Nov. 30, 1920 1,905,993 Buff Apr. 25, 1933 1,958,406 Darrah May 15, 1934 2,302,185 Campbell, Jr Nov. 17, 1942 2,357,354 Penney Sept. 5, 1944 2,357,355 Penney Sept. 5, 1944 

